What's your definition? The Lieber Code in 1863 marked a change in the laws of War (Dunmore's offer of Freedom for slaves created an opinion in US freeing slaves as a war crime). So if you count that then lots and lots of war crimes. Indeed the Lieber code may have been commissioned to justify the emancipation proclamation.

see this which includes an interview with Mr Witt who wrote the book on this. http://backstoryradio.org/shows/rules-of-engagement-ethics-in-warfare-2/

i get this is not really what your looking for but it technically falls under the purview and is in my opinion too interesting not to share